When installing a directional antenna, it is important to place it toward an appropriate direction in order to maximize the reception level. Currently, when adjusting the antenna orientation, a worker seeks the orientation with the maximum reception level by a process of trial and error by changing the antenna orientation in a step-by-step manner and installs the antenna in that orientation.
However, because two orientations, the elevation and the azimuth, need to be set to adjust the antenna orientation, it is extremely difficult in practice to set the antenna orientation toward the direction in which the maximum reception level can be achieved. It is time-consuming work to set the antenna toward the direction with the maximum reception level in a step-by-step manner by making fine adjustment of the elevation and the azimuth by checking the reception level each time. Since radio waves at millimeter-wave frequencies have been used recently, it is required to set the antenna orientation with respect to the wave source antenna with such accuracy as if going through the eye of a needle. For example, extremely fine angle adjustment of 1.0° or less, such as 0.4° or 0.2°, is required today. In consideration of the case of mounting the antenna on a mast or the like using mounting bracket, it should take less than one turn of a mounting screw. Considerable experience is needed for accurate adjustment of the antenna orientation by trial and error without any criteria like an index.
Methods for assisting in setting the antenna orientation toward the wave source direction are proposed (for example, Patent Literatures 1, 2 and 3).
For example, Patent Literature 1 discloses a direction finder that searches for a radio emitting source. The direction finder includes a direction finding array antenna and a camera mounted on the array antenna. A lens of the camera is aligned so that its optical axis is substantially orthogonal to the vertical plane of the array antenna. In this structure, an image of an object that is assumed to be a radio emitting source is taken by the camera. Further, a received signal that is received by the array antenna is visualized by a technique such as radio holography and output as a wave source image. Then, a screen, on which the camera image and the wave source image are displayed and superimposed on one another, is provided to a worker. By viewing the screen, the worker can specify the object as the radio emitting source.
In Patent Literatures 2 and 3, a camera that is aligned with respect to an antenna is mounted on the antenna, and the camera is used as a sighting device. A radio emitting source is specified by the camera, and the orientation of the antenna is adjusted so that the radio emitting source comes at the center of the screen. In this manner, specifying the radio emitting source by the camera or using the camera as the sighting device are helpful in adjusting the antenna orientation.